Hazardous material repository systems and methods

ABSTRACT

Techniques for storing nuclear waste include placing a plurality of nuclear waste portions into an inner volume of a housing of a nuclear waste canister configured to store the nuclear waste portions in a hazardous waste repository of a directional drillhole formed in a subterranean formation; substantially filling voids within the inner volume and between the plurality of nuclear waste portions with a solid or semi-solid granular material; and sealing the inner volume of the nuclear waste canister to enclose the plurality of nuclear waste portions and the solid or semi-solid granular material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to: U.S.Provisional Patent Application Ser. No. 62/808,588, filed on Feb. 21,2019; U.S. Provisional Patent Application Ser. No. 62/808,545, filed onFeb. 21, 2019; and U.S. Provisional Patent Application Ser. No.62/833,097, filed on Apr. 12, 2019. The entire contents of each of theprevious applications are incorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to hazardous material repository systems andmethods.

BACKGROUND

Hazardous material, such as radioactive waste, is often placed inlong-term, permanent, or semi-permanent storage so as to prevent healthissues among a population living near the stored waste. Such hazardouswaste storage is often challenging, for example, in terms of storagelocation identification and surety of containment. For instance, thesafe storage of nuclear waste (e.g., spent nuclear fuel, whether fromcommercial power reactors, test reactors, or even high-grade militarywaste) is considered to be one of the outstanding challenges of energytechnology. Safe storage of the long-lived radioactive waste is a majorimpediment to the adoption of nuclear power in the United States andaround the world. Conventional waste storage methods have emphasized theuse of tunnels, and is exemplified by the design of the Yucca Mountainstorage facility. Other techniques include boreholes, including verticalboreholes, drilled into crystalline basement rock. Other conventionaltechniques include forming a tunnel with boreholes emanating from thewalls of the tunnel in shallow formations to allow human access.

SUMMARY

In a general implementation, a nuclear waste canister includes a housingthat at least partially defines an inner volume sized to enclose aplurality of nuclear waste portions and configured to store the nuclearwaste portions in a hazardous waste repository of a directionaldrillhole formed in a subterranean formation; and a solid or semi-solidgranular material enclosed in the inner volume of the housing that atleast substantially fills voids within the inner volume and between theplurality of nuclear waste portions.

In an aspect combinable with the general implementation, the nuclearwaste portions include a plurality of spent nuclear fuel (SNF) rods ofan SNF assembly.

In another aspect combinable with any of the previous aspects, the innervolume is sized to store a single SNF assembly.

In another aspect combinable with any of the previous aspects, the solidor semi-solid granular material includes a solid powder.

In another aspect combinable with any of the previous aspects, the solidpowder includes silicon-dioxide.

In another aspect combinable with any of the previous aspects, the solidor semi-solid granular material includes a neutron-absorbing material.

Another aspect combinable with any of the previous aspects furtherincludes an impact absorber positioned within the inner volume or on anexterior surface of the housing.

In another aspect combinable with any of the previous aspects, theimpact absorber includes a crushable member or spring member.

In another aspect combinable with any of the previous aspects, theimpact absorber includes a low-corrosion material.

Another aspect combinable with any of the previous aspects furtherincludes a friction brake mounted to an end of the housing.

In another aspect combinable with any of the previous aspects, thefriction brake is mounted to the housing with a pivotable or rotatableconnection.

In another aspect combinable with any of the previous aspects, the endof the housing includes a downhole end of the housing.

In another aspect combinable with any of the previous aspects, thefriction brake includes a surface configured to contact a casinginstalled in the directional drillhole.

In another general implementation, a method for storing nuclear wasteincludes placing a plurality of nuclear waste portions into an innervolume of a housing of a nuclear waste canister configured to store thenuclear waste portions in a hazardous waste repository of a directionaldrillhole formed in a subterranean formation; substantially fillingvoids within the inner volume and between the plurality of nuclear wasteportions with a solid or semi-solid granular material; and sealing theinner volume of the nuclear waste canister to enclose the plurality ofnuclear waste portions and the solid or semi-solid granular material.

In an aspect combinable with the general implementation, the nuclearwaste portions include a plurality of spent nuclear fuel (SNF) rods ofan SNF assembly.

In another aspect combinable with any of the previous aspects, the innervolume is sized to store a single SNF assembly.

In another aspect combinable with any of the previous aspects, the solidor semi-solid granular material includes a solid powder.

In another aspect combinable with any of the previous aspects, the solidpowder includes silicon-dioxide.

In another aspect combinable with any of the previous aspects, the solidor semi-solid granular material includes a neutron-absorbing material.

In another aspect combinable with any of the previous aspects, thenuclear waste canister further includes an impact absorber positionedwithin the inner volume or on an exterior surface of the housing.

In another aspect combinable with any of the previous aspects, theimpact absorber includes a crushable member or spring member.

In another aspect combinable with any of the previous aspects, theimpact absorber includes a low-corrosion material.

In another aspect combinable with any of the previous aspects, thenuclear waste canister further includes a friction brake mounted to anend of the housing.

In another aspect combinable with any of the previous aspects, thefriction brake is mounted to the housing with a pivotable or rotatableconnection.

In another aspect combinable with any of the previous aspects, the endof the housing includes a downhole end of the housing.

In another aspect combinable with any of the previous aspects, thefriction brake includes a surface configured to contact a casinginstalled in the directional drillhole.

Another aspect combinable with any of the previous aspects furtherincludes moving the sealed nuclear waste canister into the hazardouswaste repository of the directional drillhole.

Another aspect combinable with any of the previous aspects furtherincludes mitigating an impact of the sealed nuclear waste canisterduring a free fall event during movement of the sealed nuclear wastecanister through the directional drillhole.

Implementations of a hazardous material storage repository according tothe present disclosure may include one or more of the followingfeatures. For example, a hazardous material storage repository accordingto the present disclosure may allow for multiple levels of containmentof hazardous material within a storage repository located thousands offeet underground, decoupled from any nearby mobile water. As anotherexample, implementations of a hazardous material canister according tothe present disclosure may withstand or reduce collisions within adirectional drillhole with other objects, including other canisters, toreduce leakage of hazardous material due to such collisions. As anotherexample, implementations of a hazardous material canister according tothe present disclosure may be more easily and efficiently loaded withradioactive waste, e.g., without requiring such loading to be completedwholly within a hot room. As another example, a hazardous materialstorage repository according to the present disclosure may beconstructed such that a free-falling hazardous material canister doesnot damage itself or other objects within a directional drillhole evenindependently of a construction of the canister, itself.

The details of one or more implementations of the subject matterdescribed in this disclosure are set forth in the accompanying drawingsand the description below. Other features, aspects, and advantages ofthe subject matter will become apparent from the description, thedrawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an example implementation of ahazardous material storage repository that includes one or morehazardous material canisters according to the present disclosure.

FIGS. 2 and 3A-3D are schematic illustrations of example implementationsof a hazardous material canister according to the present disclosure.

FIGS. 4A-4B are schematic illustrations of another exampleimplementation of a hazardous material canister according to the presentdisclosure.

FIG. 5 is a schematic illustration of an example implementation of ahazardous material storage repository that includes a safety runwayportion according to the present disclosure.

DETAILED DESCRIPTION

FIG. 1 is a schematic illustration of an example implementation of ahazardous material storage repository system 100, e.g., a subterraneanlocation for the long-term (e.g., tens, hundreds, or thousands of yearsor more), but retrievable, safe and secure storage of hazardous material(e.g., radioactive material, such as nuclear waste which can be spentnuclear fuel (SNF) or high level waste, as two examples). For example,this figure illustrates the example hazardous material storagerepository system 100 once one or more canisters 126 of hazardousmaterial have been deployed in a subterranean formation 118. Asillustrated, the hazardous material storage repository system 100includes a drillhole 104 formed (e.g., drilled or otherwise) from aterranean surface 102 and through multiple subterranean layers 112, 114,116, and 118. Although the terranean surface 102 is illustrated as aland surface, terranean surface 102 may be a sub-sea or other underwatersurface, such as a lake or an ocean floor or other surface under a bodyof water. Thus, the present disclosure contemplates that the drillhole104 may be formed under a body of water from a drilling location on orproximate the body of water.

The illustrated drillhole 104 is a directional drillhole in this exampleof hazardous material storage repository system 100. For instance, thedrillhole 104 includes a substantially vertical portion 106 coupled to aradiussed or curved portion 108, which in turn is coupled to asubstantially horizontal portion 110. As used in the present disclosure,“substantially” in the context of a drillhole orientation, refers todrillholes that may not be exactly vertical (e.g., exactly perpendicularto the terranean surface 102) or exactly horizontal (e.g., exactlyparallel to the terranean surface 102), or exactly inclined at aparticular incline angle relative to the terranean surface 102. In otherwords, vertical drillholes often undulate offset from a true verticaldirection, that they might be drilled at an angle that deviates fromtrue vertical, and inclined drillholes often undulate offset from a trueincline angle. Further, in some aspects, an inclined drillhole may nothave or exhibit an exactly uniform incline (e.g., in degrees) over alength of the drillhole. Instead, the incline of the drillhole may varyover its length (e.g., by 1-5 degrees). As illustrated in this example,the three portions of the drillhole 104—the vertical portion 106, theradiussed portion 108, and the horizontal portion 110—form a continuousdrillhole 104 that extends into the Earth. As used in the presentdisclosure, the drillhole 104 (and drillhole portions described) mayalso be called wellbores. Thus, as used in the present disclosure,drillhole and wellbore are largely synonymous and refer to bores formedthrough one or more subterranean formations that are not suitable forhuman-occupancy (i.e., are too small in diameter for a human to fitthere within).

The illustrated drillhole 104, in this example, has a surface casing 120positioned and set around the drillhole 104 from the terranean surface102 into a particular depth in the Earth. For example, the surfacecasing 120 may be a relatively large-diameter tubular member (or stringof members) set (e.g., cemented) around the drillhole 104 in a shallowformation. As used herein, “tubular” may refer to a member that has acircular cross-section, elliptical cross-section, or other shapedcross-section. For example, in this implementation of the hazardousmaterial storage repository system 100, the surface casing 120 extendsfrom the terranean surface through a surface layer 112. The surfacelayer 112, in this example, is a geologic layer comprised of one or morelayered rock formations. In some aspects, the surface layer 112 in thisexample may or may not include freshwater aquifers, salt water or brinesources, or other sources of mobile water (e.g., water that movesthrough a geologic formation). In some aspects, the surface casing 120may isolate the drillhole 104 from such mobile water, and may alsoprovide a hanging location for other casing strings to be installed inthe drillhole 104. Further, although not shown, a conductor casing maybe set above the surface casing 120 (e.g., between the surface casing120 and the surface 102 and within the surface layer 112) to preventdrilling fluids from escaping into the surface layer 112.

As illustrated, a production casing 122 is positioned and set within thedrillhole 104 downhole of the surface casing 120. Although termed a“production” casing, in this example, the casing 122 may or may not havebeen subject to hydrocarbon production operations. Thus, the casing 122refers to and includes any form of tubular member that is set (e.g.,cemented) in the drillhole 104 downhole of the surface casing 120. Insome examples of the hazardous material storage repository system 100,the production casing 122 may begin at an end of the radiussed portion108 and extend throughout the horizontal portion 110. The casing 122could also extend into the radiussed portion 108 and into the verticalportion 106.

As shown, cement 130 is positioned (e.g., pumped) around the casings 120and 122 in an annulus between the casings 120 and 122 and the drillhole104. The cement 130, for example, may secure the casings 120 and 122(and any other casings or liners of the drillhole 104) through thesubterranean layers under the terranean surface 102. In some aspects,the cement 130 may be installed along the entire length of the casings(e.g., casings 120 and 122 and any other casings), or the cement 130could be used along certain portions of the casings if adequate for aparticular drillhole 104. The cement 130 can also provide an additionallayer of confinement for the hazardous material in canisters 126.

The drillhole 104 and associated casings 120 and 122 may be formed withvarious example dimensions and at various example depths (e.g., truevertical depth, or TVD). For instance, a conductor casing (not shown)may extend down to about 120 feet TVD, with a diameter of between about28 in. and 60 in. The surface casing 120 may extend down to about 2500feet TVD, with a diameter of between about 22 in. and 48 in. Anintermediate casing (not shown) between the surface casing 120 andproduction casing 122 may extend down to about 8000 feet TVD, with adiameter of between about 16 in. and 36 in. The production casing 122may extend inclinedly (e.g., to case the horizontal portion 110) with adiameter of between about 11 in. and 22 in. The foregoing dimensions aremerely provided as examples and other dimensions (e.g., diameters, TVDs,lengths) are contemplated by the present disclosure. For example,diameters and TVDs may depend on the particular geological compositionof one or more of the multiple subterranean layers (112, 114, 116, and118), particular drilling techniques, as well as a size, shape, ordesign of a hazardous material canister 126 that contains hazardousmaterial to be deposited in the hazardous material storage repositorysystem 100. In some alternative examples, the production casing 122 (orother casing in the drillhole 104) could be circular in cross-section,elliptical in cross-section, or some other shape.

As illustrated, the vertical portion 106 of the drillhole 104 extendsthrough subterranean layers 112, 114, and 116, and, in this example,lands in a subterranean layer 118. As discussed above, the surface layer112 may or may not include mobile water. In this example, a mobile waterlayer 114 is below the surface layer 112 (although surface layer 112 mayalso include one or more sources of mobile water or liquid). Forinstance, mobile water layer 114 may include one or more sources ofmobile water, such as freshwater aquifers, salt water or brine, or othersource of mobile water. In this example of hazardous material storagerepository system 100, mobile water may be water that moves through asubterranean layer based on a pressure differential across all or a partof the subterranean layer. For example, the mobile water layer 114 maybe a permeable geologic formation in which water freely moves (e.g., dueto pressure differences or otherwise) within the layer 114. In someaspects, the mobile water layer 114 may be a primary source ofhuman-consumable water in a particular geographic area. Examples of rockformations of which the mobile water layer 114 may be composed includeporous sandstones and limestones, among other formations.

Other illustrated layers, such as the impermeable layer 116 and thestorage layer 118, may include immobile water. Immobile water, in someaspects, is water (e.g., fresh, salt, brine), that is not fit for humanor animal consumption, or both. Immobile water, in some aspects, may bewater that, by its motion through the layers 116 or 118 (or both),cannot reach the mobile water layer 114, terranean surface 102, or both,within 10,000 years or more (such as to 1,000,000 years).

Below the mobile water layer 114, in this example implementation ofhazardous material storage repository system 100, is an impermeablelayer 116. The impermeable layer 116, in this example, may not allowmobile water to pass through. Thus, relative to the mobile water layer114, the impermeable layer 116 may have low permeability, e.g., on theorder of nanodarcy permeability. Additionally, in this example, theimpermeable layer 116 may be a relatively non-ductile (i.e., brittle)geologic formation. One measure of non-ductility is brittleness, whichis the ratio of compressive stress to tensile strength. In someexamples, the brittleness of the impermeable layer 116 may be betweenabout 20 MPa and 40 MPa.

As shown in this example, the impermeable layer 116 is shallower (e.g.,closer to the terranean surface 102) than the storage layer 118. In thisexample rock formations of which the impermeable layer 116 may becomposed include, for example, certain kinds of sandstone, mudstone,clay, and slate that exhibit permeability and brittleness properties asdescribed above. In alternative examples, the impermeable layer 116 maybe deeper (e.g., further from the terranean surface 102) than thestorage layer 118. In such alternative examples, the impermeable layer116 may be composed of an igneous rock, such as granite.

Below the impermeable layer 116 is the storage layer 118. The storagelayer 118, in this example, may be chosen as the landing for thehorizontal portion 110, which stores the hazardous material, for severalreasons. Relative to the impermeable layer 116 or other layers, thestorage layer 118 may be thick, e.g., between about 100 and 200 feet oftotal vertical thickness. Thickness of the storage layer 118 may allowfor easier landing and directional drilling, thereby allowing thehorizontal portion 110 to be readily emplaced within the storage layer118 during constructions (e.g., drilling). If formed through anapproximate horizontal center of the storage layer 118, the horizontalportion 110 may be surrounded by about 50 to 100 feet of the geologicformation that comprises the storage layer 118. Further, the storagelayer 118 may also have only immobile water, e.g., due to a very lowpermeability of the layer 118 (e.g., on the order of milli- ornanodarcys). In addition, the storage layer 118 may have sufficientductility, such that a brittleness of the rock formation that comprisesthe layer 118 is between about 3 MPa and 10 MPa. Examples of rockformations of which the storage layer 118 may be composed include: shaleand anhydrite. Further, in some aspects, hazardous material may bestored below the storage layer, even in a permeable formation such assandstone or limestone, if the storage layer is of sufficient geologicproperties to isolate the permeable layer from the mobile water layer114.

In some examples implementations of the hazardous material storagerepository system 100, the storage layer 118 (and/or the impermeablelayer 116) is composed of shale. Shale, in some examples, may haveproperties that fit within those described above for the storage layer118. For example, shale formations may be suitable for a long-termconfinement of hazardous material (e.g., in the hazardous materialcanisters 126), and for their isolation from mobile water layer 114(e.g., aquifers) and the terranean surface 102. Shale formations may befound relatively deep in the Earth, typically 3000 feet or greater, andplaced in isolation below any fresh water aquifers. Other formations mayinclude salt or other impermeable formation layer.

Shale formations (or salt or other impermeable formation layers), forinstance, may include geologic properties that enhance the long-term(e.g., thousands of years) isolation of material. Such properties, forinstance, have been illustrated through the long term storage (e.g.,tens of millions of years) of hydrocarbon fluids (e.g., gas, liquid,mixed phase fluid) without escape of substantial fractions of suchfluids into surrounding layers (e.g., mobile water layer 114). Indeed,shale has been shown to hold natural gas for millions of years or more,giving it a proven capability for long-term storage of hazardousmaterial. Example shale formations (e.g., Marcellus, Eagle Ford,Barnett, and otherwise) has stratification that contains many redundantsealing layers that have been effective in preventing movement of water,oil, and gas for millions of years, lacks mobile water, and can beexpected (e.g., based on geological considerations) to seal hazardousmaterial (e.g., fluids or solids) for thousands of years after deposit.

In some aspects, the formation of the storage layer 118 and/or theimpermeable layer 116 may form a leakage barrier, or barrier layer tofluid leakage that may be determined, at least in part, by the evidenceof the storage capacity of the layer for hydrocarbons or other fluids(e.g., carbon dioxide) for hundreds of years, thousands of years, tensof thousands of years, hundreds of thousands of years, or even millionsof years. For example, the barrier layer of the storage layer 118 and/orimpermeable layer 116 may be defined by a time constant for leakage ofthe hazardous material more than 10,000 years (such as between about10,000 years and 1,000,000 years) based on such evidence of hydrocarbonor other fluid storage.

Shale (or salt or other impermeable layer) formations may also be at asuitable depth, e.g., between 3000 and 12,000 feet TVD. Such depths aretypically below ground water aquifer (e.g., surface layer 112 and/ormobile water layer 114). Further, the presence of soluble elements inshale, including salt, and the absence of these same elements in aquiferlayers, demonstrates a fluid isolation between shale and the aquiferlayers.

Another particular quality of shale that may advantageously lend itselfto hazardous material storage is its clay content, which, in someaspects, provides a measure of ductility greater than that found inother, impermeable rock formations (e.g., impermeable layer 116). Forexample, shale may be stratified, made up of thinly alternating layersof clays (e.g., between about 20-30% clay by volume) and other minerals.Such a composition may make shale less brittle and, thus lesssusceptible to fracturing (e.g., naturally or otherwise) as compared torock formations in the impermeable layer (e.g., dolomite or otherwise).For example, rock formations in the impermeable layer 116 may havesuitable permeability for the long term storage of hazardous material,but are too brittle and commonly are fractured. Thus, such formationsmay not have sufficient sealing qualities (as evidenced through theirgeologic properties) for the long term storage of hazardous material.

The present disclosure contemplates that there may be many other layersbetween or among the illustrated subterranean layers 112, 114, 116, and118. For example, there may be repeating patterns (e.g., vertically), ofone or more of the mobile water layer 114, impermeable layer 116, andstorage layer 118. Further, in some instances, the storage layer 118 maybe directly adjacent (e.g., vertically) the mobile water layer 114,i.e., without an intervening impermeable layer 116. In some examples,all or portions of the radiussed drillhole 108 and the horizontaldrillhole 110 may be formed below the storage layer 118, such that thestorage layer 118 (e.g., shale or other geologic formation withcharacteristics as described herein) is vertically positioned betweenthe horizontal drillhole 110 and the mobile water layer 114.

In this example, the horizontal portion 110 of the drillhole 104includes a storage area in a distal part of the portion 110 into whichhazardous material may be retrievably placed for long-term storage. Forexample, a work string (e.g., tubing, coiled tubing, wireline, orotherwise) or other downhole conveyance (e.g., tractor) may be movedinto the cased drillhole 104 to place one or more (three shown but theremay be more or less) hazardous material canisters 126 into long term,but in some aspects, retrievable, storage in the portion 110.

Each canister 126 may enclose hazardous material (shown as material145). Such hazardous material, in some examples, may be biological orchemical waste or other biological or chemical hazardous material. Insome examples, the hazardous material may include nuclear material, suchas SNF recovered from a nuclear reactor (e.g., commercial power or testreactor) or military nuclear material. Spent nuclear fuel, in the formof nuclear fuel pellets, may be taken from the reactor and not modified.Nuclear fuel pellet are solid, although they can contain and emit avariety of radioactive gases including tritium (13 year half-life),krypton-85 (10.8 year half-life), and carbon dioxide containing C-14(5730 year half-life). Other hazardous material 145 may include, forexample, radioactive liquid, such as radioactive water from a commercialpower (or other) reactor.

In some aspects, the storage layer 118 should be able to contain anyradioactive output (e.g., gases) within the layer 118, even if suchoutput escapes the canisters 126. For example, the storage layer 118 maybe selected based on diffusion times of radioactive output through thelayer 118. For example, a minimum diffusion time of radioactive outputescaping the storage layer 118 may be set at, for example, fifty times ahalf-life for any particular component of the nuclear fuel pellets.Fifty half-lives as a minimum diffusion time would reduce an amount ofradioactive output by a factor of 1×10¹⁵. As another example, setting aminimum diffusion time to thirty half-lives would reduce an amount ofradioactive output by a factor of one billion.

For example, plutonium-239 is often considered a dangerous waste productin SNF because of its long half-life of 24,100 years. For this isotope,50 half-lives would be 1.2 million years. Plutonium-239 has lowsolubility in water, is not volatile, and as a solid, its diffusion timeis exceedingly small (e.g., many millions of years) through a matrix ofthe rock formation that comprises the illustrated storage layer 118(e.g., shale or other formation). The storage layer 118, for examplecomprised of shale, may offer the capability to have such isolationtimes (e.g., millions of years) as shown by the geological history ofcontaining gaseous hydrocarbons (e.g., methane and otherwise) forseveral million years. In contrast, in conventional nuclear materialstorage methods, there was a danger that some plutonium might dissolvein a layer that comprised mobile ground water upon confinement escape.

In some aspects, the drillhole 104 may be formed for the primary purposeof long-term storage of hazardous materials. In alternative aspects, thedrillhole 104 may have been previously formed for the primary purpose ofhydrocarbon production (e.g., oil, gas). For example, storage layer 118may be a hydrocarbon bearing formation from which hydrocarbons wereproduced into the drillhole 104 and to the terranean surface 102. Insome aspects, the storage layer 118 may have been hydraulicallyfractured prior to hydrocarbon production. Further in some aspects, theproduction casing 122 may have been perforated prior to hydraulicfracturing. In such aspects, the production casing 122 may be patched(e.g., cemented) to repair any holes made from the perforating processprior to a deposit operation of hazardous material. In addition, anycracks or openings in the cement between the casing and the drillholecan also be filled at that time.

As further shown in FIG. 1, a backfill material 140 may be positioned orcirculated into the drillhole 104. In this example, the backfillmaterial 140 surrounds the canisters 126 and may have a level thatextends uphole to at or near a drillhole seal 134 (e.g., permanentpacker, plug, or other seal). In some aspects, the backfill material 140may absorb radioactive energy (e.g., gamma rays or other energy). Insome aspects, the backfill material 140 may have a relatively lowthermal conductivity, thereby acting as an insulator between thecanisters 126 and the casings.

As further shown in FIG. 1, another backfill material 150 may bepositioned or placed within one or more of the canisters 126 to surroundthe hazardous material 145. In some aspects, the backfill material 150may absorb radioactive energy (e.g., gamma rays or other energy). Insome aspects, the backfill material 150 may have a relatively lowthermal conductivity, thereby acting as an insulator between thehazardous material 145 and the canister 126. In some aspects, thebackfill material 150 may also provide a stiffening attribute to thecanister 126, e.g., reducing crushability, deformation, or other damageto the canister 126.

In some aspects, one or more of the previously described components ofthe system 100 may combine to form an engineered barrier of thehazardous waste material repository 100. For example, in some aspects,the engineered barrier is comprised of one, some, or all of thefollowing components: the storage layer 118, the casing 130, thebackfill material 140, the canister 126, the backfill material 150, theseal 134, and the hazardous material 145, itself. In some aspects, oneor more of the engineered barrier components may act (or be engineeredto act) to: prevent or reduce corrosion in the drillhole 104, prevent orreduce escape of the hazardous material 145; reduce or prevent thermaldegradation of one or more of the other components; and other safetymeasures to ensure that the hazardous material 145 does not reach themobile water layer 114 (or surface layer 112, including the terraneansurface 102).

FIG. 2 is a schematic illustration of a hazardous material canister 200according to the present disclosure. In some aspects, the hazardousmaterial canister 200 may be used as the hazardous material canister 126shown in the hazardous material storage repository system 100 of FIG. 1.In some aspects, the hazardous material canister 200 may enclose andstore nuclear or radioactive waste, such as SNF or high level waste. Asdescribed in the example emplacement process of the canisters 126 intothe hazardous material storage repository system 100 of FIG. 1, thehazardous material canister 200 may be placed in a human-unoccupiabledeep directional drillhole (e.g., drillhole 104) for long term (e.g.,hundreds if not thousands of years) storage. During the emplacementprocess, the hazardous material canister 200 may be moved into thedirectional drillhole 104 on a conveyance cable, such as, for example, awireline cable. When the hazardous material canister 200 is loweredthrough the vertical portion 106 of the directional drillhole 104, thereis a possibility that the cable (or a connection between the canister200 and the cable) that supports the canister 200 may fail. Uponfailure, the canister 200 will accelerate downward (e.g., in free fall)in the vertical portion 106 of the directional drillhole 104 (e.g.,through a fluid in the drillhole 104).

If the directional drillhole 104 has a kickoff point for the transitionportion 108 (e.g., a transition to a horizontal or nearly-horizontaldrillhole portion from the vertical portion 106), then the canister 200will slow and eventually stop in the horizontal drillhole portion 110.However, if the hazardous material storage repository system 100 haspreviously been filled with other hazardous material canisters 200, thenthe free-falling canister 200 could impact a stationary canister 200with resulting damage to both hazardous material canisters 200. If thehazardous waste material (e.g., nuclear waste) inside the canister 200is highly radioactive, there is a danger of release of this materialinto the drillhole portion 110, which could potentially lead to releaseinto a surrounding subterranean formation 118, and possibly mobile waterin such a formation or other formations (e.g., subterranean formation112). The illustrated implementation of hazardous material canister 200includes one or more features that, e.g., may reduce or preventpotential damage to the canister 200 due to a free-fall in the deepdirectional drillhole 104. For example, the hazardous material canister200 may maintain its structural integrity and its value as an“engineered barrier” to the release of hazardous material duringfree-fall and/or impact with another object in the drillhole 104.

As shown in FIG. 2, the hazardous material canister 200 includes ahousing 202 that is comprised of a middle portion 204 to which a top (orlid) 206 and bottom 208 are coupled (e.g., subsequent to enclosing thehazardous waste) to form an inner volume 212. In this example, thehazardous material is one or more SNF assemblies 210 that include SNFrods 214. In an example implementation, a material 216 (e.g., granularor particulate) is emplaced within the inner volume 212 of the canister200 (surrounding the SNF assembly 210 (or assemblies 210) and even theSNF rods 214). This material 216 may be sand or another granularmaterial (collectively referred to as “sand”) and may be placed into thecanister 200 to fill voids that surround the SNF assembly 210 (or rods214). For example, in the case of the hazardous material being an SNFassembly comprised of SNF rods (in whole or part), then the SNF rods 214occupy only about ⅓ or less of the inner volume 212 of the canister 200.A sudden impact on the canister 200 (e.g., due to a free-fall event)could cause the SNF rods 214 to buckle and break. Buckling, in somecases, occurs (during a free-fall situation) when a front (bottom ordownhole) end of the SNF rod 214 is suddenly stopped (e.g., due to acollision). The rest of the SNF rod 214 initially continues downward dueto momentum. If the SNF rod 214 is completely symmetric, then the SNFrod 214 will compress, but slight deviations from symmetry are usuallypresent, and so the SNF rod 214 tends to bend. In this deceleratingsituation, that bending becomes unstable and the bend increases rapidlyuntil the SNF rod 214 breaks.

To prevent buckling, aspects of the hazardous material canister 200 mayprovide minimal support for the sides of the SNF rods 214. In somecases, the structure of the SNF assembly 210 that holds the SNF rods 214provides lateral support. But more resistance to buckling can beobtained by filling the voids in the SNF assembly 210 with the material216 (e.g., sand or other a relatively dense material). In some aspects,the material 216 can be silicon-dioxide, clay, crushed rock, cement,epoxy, or other powder of a solid. The material 216 provides support ofthe sides of the SNF rods 214 in a collision that prevents or helpsprevent the SNF rods 214 from buckling. In some aspects, the preventionof buckling may not require a very strong material since the initialhorizontal bucking force is small, so many materials could be used.

In alternative aspects, a liquid or gel may be used as the material 216to fill the voids in the inner volume 212 not occupied by the SNFassembly 210. The liquid or gel may provide less resistance to bucklingrelative to a solid.

The material 216 could achieve other purposes. For example, if thehazardous waste (i.e., SNF assembly 210) has sufficient concentration offissionable material (e.g., U-235 or Pu-239), then there may be dangerof a “criticality accident;” that is, a chain reaction taking placeamong these isotopes. The presence of water may increase the danger,since water acts as a “moderator” that slows neutrons and increases thelikelihood that a neutron will trigger a fission. The material 216 canreduce this risk if it contains suitable amounts of neutron absorbers.Such absorbers are boron, cadmium, and cobalt, as some examples. Thesecan be included (e.g., as part of the granular, solid, or liquidmaterial 216) as metals or as compounds.

The material 216 that mitigates or helps mitigate damage to the SNFassembly 210 during transport and emplacement in the directionaldrillhole 104 may serve additional functions. For example, the material216 may have thermal conduction qualities that effectively allow heat tobe transferred from the SNF 210 to the housing 202 (and ultimately tothe geologic environment). Materials like quartz/sand and/or bentonite,or a mixture of the two in some favorable proportion can serve thisfunction as or as mixed in the material 216. Both have suitable thermalconduction characteristics. The thermal conductivity of thequartz/bentonite mixture may maintain lower temperatures inside thehazardous material canister 200.

As another example, in some aspects, with bentonite as or mixed with thematerial 216, the material 216 may include radionuclide sorptivequalities. In addition, by maintaining lower temperatures inside thehazardous material canister 200, such lower temperatures may keep thebentonite from transitioning from a smectite- to an illite-type clay.Such a transition is time and/or temperature dependent, and once itoccurs, the bentonite no longer has the capacity to incorporate waterinto interlayer structures. The bentonite may also lose all or part of acapacity to sorb and retard radionuclides.

In some aspects, rather than bentonite being or being part of thematerial 216, one or more zeolites could be mixed with quartz sand (orreplace the sand) of the material 216. For example, zeolites are ringstructure silicate minerals that are porous and can be used as molecularsieves. Zeolites can be manufactured and tailored to have structuralpores of different sizes to effectively trap different radionuclides.There are zeolites “doped” with (silver) Ag+ ions that are designedspecifically to allow I-ions (Iodine ions) to enter the zeolitestructure. When the I-ions bond with the Ag+ to form AgI, the largermolecular size irreversibly traps the Iodine in the zeolite, effectivelyimmobilizing the Iodine. Other zeolites could target differentradionuclides in a similar fashion.

In some aspects, inclusion of the material 216, such as sand, in theinner volume 212 of the hazardous material canister 200 may also preventcollapse of the canister 200 in the event of a rock collapse (e.g.,collapse of the horizontal drillhole portion 110, including the casing(if any) by the surrounding subterranean formation). For example, whenthe hazardous material canister 200 is filled with the material 216, thematerial 216 may offer extremely strong resistance to crushing. Thus,when a strong force is applied to the canister 200 (e.g., fromcollapsing rock) the canister 200 may not bend because of the resistanceof the material 216 to collapse.

As shown in FIG. 2, the example implementation of the hazardous materialcanister 200 also includes an impact absorber 250 that includes a bumper252 that is coupled to the housing 202 of the hazardous materialcanister 200 through a joint 256 connected to the housing (e.g., throughan extension 258). As shown, the bumper 252 is positioned at a bottom(downhole) end of the canister 200. In some aspects, the bumper 252 may,alternatively, be built into or part of the bottom 208 of the housing202. The bumper 252 may absorb impact in a free-fall collision of thecanister 200 with, e.g., another hazardous material canister in thedrillhole 104, the casing 122 (as shown in this figure) or other object.In some aspects, the bumper 252 may also mitigate acceleration of afree-falling canister 200 from impact at the front (downhole) end. Insome aspects, as shown, the impact absorber 252 can be or include acrushable material or a spring 254, either internal to the bumper 252 orsurrounding the bumper 252.

In some aspects, the impact absorber 252 may assure or help assuresafety of the canister 200 during lowering into the directionaldrillhole 104. For example, when the canister 200 is in place in arepository of the horizontal drillhole portion 110, there may not be acontinuing danger of a fall, so the bumper 252 may no longer be needed.When the canister 200 is emplaced, the bumper 252 (and joint 256, andextension 258) may become a liability as a corrosion point that couldcreate hydrogen gas within the casing 122. In a sealed environment suchas the drillhole 104, such corrosion could cause an increase in pressurefrom corrosion volume expansion. For these reasons, in some aspects, thebumper 252 (and other illustrated components) may be made of alow-corrosion material. Possible materials include graphite, titanium,tungsten-carbide cobalt, or nickel-chromium compounds such as Inconel.

In some aspects, the impact absorber 252 may also include or act as afriction brake. For instance, when the hazardous material canister 200is falling freely has shown by arrow 262) in the fluid-filled casing(with fluid 260 shown in the drillhole portion 106), the canister 200may be unstable against tipping. In some cases, tipping brings the front(downhole) end of the canister 200 into contact with the casing 122. Ina high velocity fall, the friction at this contact point can cause localheating and can apply a force on the canister 200 that could damage thecanister integrity. The impact absorber 252 (or separate friction brakeattached to the bumper 252) may include a friction brake as shownattached to an exterior of the housing 202 of the canister 200. Forexample, a section at the front (downhole) end of the canister 200 thatis most prone to friction with the casing 122 can include the frictionbrake to mitigate damage from friction to the canister 200 in the caseof a free fall (or otherwise). The friction brake may also utilizefriction to slow the acceleration of a falling canister 200. In someaspects, a portion of the impact absorber 252 that acts as the frictionbrake (or the separate friction brake component of the bumper 252) canbe curved (to minimize the friction), or rough or pointed to maximizethe friction and provide a stronger limit on the velocity of the fallingcanister 200.

In some aspects, the friction brake could be part of the housing 202(e.g., on the downhole end). If the brake is rigidly attached to thecanister 200, then rotation would be an extension of that of thecanister 200. As shown, the friction brake (as part of the impactabsorber 252 or otherwise) could also be attached to the canister 200with the joint 256 that allows relative rotation.

FIG. 3A is a schematic illustration of a hazardous material canister 300according to the present disclosure. In some aspects, the hazardousmaterial canister 300 may be used as the hazardous material canister 126shown in the hazardous material storage repository system 100 of FIG. 1.In some aspects, the hazardous material canister 300 may enclose andstore nuclear or radioactive waste, such as SNF or high level waste. Asdescribed in the example emplacement process of the canisters 126 intothe hazardous material storage repository system 100 of FIG. 1, thehazardous material canister 300 may be placed in a human-unoccupiabledeep directional drillhole (e.g., drillhole 104) for long term (e.g.,hundreds if not thousands of years) storage. During the emplacementprocess, the hazardous material canister 300 may be moved into thedirectional drillhole 104 on a conveyance cable, such as, for example, awireline cable. When the hazardous material canister 300 is loweredthrough the vertical portion 106 of the directional drillhole 104, thereis a possibility that the cable (or a connection between the canister300 and the cable) that supports the canister 300 may fail. Uponfailure, the canister 300 will accelerate downward (e.g., in free fall)in the vertical portion 106 of the directional drillhole 104 (e.g.,through a fluid in the drillhole 104). Further, although notspecifically shown in FIG. 3A, the hazardous material canister 300 mayinclude certain components as described with reference to FIG. 2, suchas, for example, the material 216 and the impact absorber 252 (with orwithout a friction brake).

If the directional drillhole 104 has a kickoff point for the transitionportion 108 (e.g., a transition to a horizontal or nearly-horizontaldrillhole portion from the vertical portion 106), then the canister 300will slow and eventually stop in the horizontal drillhole portion 110.However, if the hazardous material storage repository system 100 haspreviously been filled with other hazardous material canisters 300, thenthe free-falling canister 300 could impact a stationary canister 300with resulting damage to both hazardous material canisters 300. If thehazardous waste material (e.g., nuclear waste) inside the canister 300is highly radioactive, there is a danger of release of this materialinto the drillhole portion 110, which could potentially lead to releaseinto a surrounding subterranean formation 118, and possibly mobile waterin such a formation or other formations (e.g., subterranean formation112). The illustrated implementation of hazardous material canister 300includes one or more features that, e.g., may reduce or preventpotential damage to the canister 300 due to a free-fall in the deepdirectional drillhole 104. For example, the hazardous material canister300 may maintain its structural integrity and its value as an“engineered barrier” to the release of hazardous material duringfree-fall and/or impact with another object in the drillhole 104.

As shown in FIG. 3A, the hazardous material canister 300 includes ahousing 302 that is comprised of a middle portion 304 to which a top (orlid) 306 and bottom 308 are coupled (e.g., subsequent to enclosing thehazardous waste) to form an inner volume 312. In this example, thehazardous material is one or more SNF assemblies 310 that include SNFrods (not specifically shown here). As shown, the hazardous materialcanister 300 also includes two or more centralizers 314 that areattached (e.g., radially around the canister 300) to the housing 302. Insome aspects, there may be three centralizers 314 attached to thehousing 302 and spaced 120° radially apart.

In this example, each centralizer 314 includes spacers (also called“arms”) 316 that are either spring-loaded or deployable to bias against,e.g., the casing 122 as shown. In this example, the centralizers 314that circumscribe the hazardous material canister 300 operate duringdeployment of the canister 300 to hold the canister 300 near a radialcenterline 318 of the vertical drillhole portion 106 (and otherdrillhole portions) to provide space between the canister 300 and thecasing 122. Thus, during operation, the arms 316 of the centralizers 314are biased or deployed to contact the casing 122 and align a radialcenterline of the canister 300 with the centerline 318. In this example,the centralizer arms 314 may be made of spring steel or otherwise biasedby springs outward against the casing 122. The centralizers 314, in someaspects, can reduce the velocity that a falling canister 300 may reachin free-fall through frictional contact with the casing 122, therebygenerating a frictional force that opposes the free-fall (caused by theforce of gravity) within a fluid 319 in the drillhole portion 106.

FIG. 3B is a schematic illustration of a hazardous material canister 320according to the present disclosure. In some aspects, the hazardousmaterial canister 320 may be used as the hazardous material canister 126shown in the hazardous material storage repository system 100 of FIG. 1.In some aspects, the hazardous material canister 320 may enclose andstore nuclear or radioactive waste, such as SNF or high level waste. Asdescribed in the example emplacement process of the canisters 126 intothe hazardous material storage repository system 100 of FIG. 1, thehazardous material canister 320 may be placed in a human-unoccupiabledeep directional drillhole (e.g., drillhole 104) for long term (e.g.,hundreds if not thousands of years) storage. During the emplacementprocess, the hazardous material canister 320 may be moved into thedirectional drillhole 104 on a conveyance cable, such as, for example, awireline cable. When the hazardous material canister 320 is loweredthrough the vertical portion 106 of the directional drillhole 104, thereis a possibility that the cable (or a connection between the canister320 and the cable) that supports the canister 320 may fail. Uponfailure, the canister 320 will accelerate downward (e.g., in free fall)in the vertical portion 106 of the directional drillhole 104 (e.g.,through a fluid in the drillhole 104). Further, although notspecifically shown in FIG. 3B, the hazardous material canister 320 mayinclude certain components as described with reference to FIG. 2, suchas, for example, the material 216 and the impact absorber 252 (with orwithout a friction brake), as well as certain components as describedwith reference to FIG. 3A, such as, for example, the centralizers 314.

If the directional drillhole 104 has a kickoff point for the transitionportion 108 (e.g., a transition to a horizontal or nearly-horizontaldrillhole portion from the vertical portion 106), then the canister 320will slow and eventually stop in the horizontal drillhole portion 110.However, if the hazardous material storage repository system 100 haspreviously been filled with other hazardous material canisters 320, thenthe free-falling canister 320 could impact a stationary canister 320with resulting damage to both hazardous material canisters 320. If thehazardous waste material (e.g., nuclear waste) inside the canister 320is highly radioactive, there is a danger of release of this materialinto the drillhole portion 110, which could potentially lead to releaseinto a surrounding subterranean formation 118, and possibly mobile waterin such a formation or other formations (e.g., subterranean formation112). The illustrated implementation of hazardous material canister 320includes one or more features that, e.g., may reduce or preventpotential damage to the canister 320 due to a free-fall in the deepdirectional drillhole 104. For example, the hazardous material canister320 may maintain its structural integrity and its value as an“engineered barrier” to the release of hazardous material duringfree-fall and/or impact with another object in the drillhole 104.

As shown in FIG. 3B, the hazardous material canister 320 includes ahousing 322 that is comprised of a middle portion 324 to which a top (orlid) 326 and bottom 328 are coupled (e.g., subsequent to enclosing thehazardous waste) to form an inner volume 332. In this example, thehazardous material is one or more SNF assemblies 330 that include SNFrods (not specifically shown here). In this example, the hazardousmaterial canister 320 also includes a disc (also called a brake) 334that is coupled to a downhole end of the housing 322. In this example,therefore, a velocity of the hazardous material canister 320 infree-fall may be limited or reduced through the brake 334 driven by ahigh flow of the liquid 336 in the drillhole 106 relative to thecanister movement through the drillhole 106 during free-fall.

As shown in FIG. 3B, the brake 334 (which may be made from the samematerial as the housing 322 or a different material) may have a radialcross-section area that is larger than a radial cross-section area ofthe canister 320. For example, in some aspects, a diameter of the brake334 may be smaller than but almost as large as a diameter of the casing122. In some aspects, however, a size of the brake 334 (and surfacefinish of the brake 334) may be such that small discontinuities in theinner surface of the casing 122 do not impede the placement (e.g.,normal, controlled movement) of the canister. This can be achieved, forexample, by having an outer edge of the brake 334 (e.g., a radialcircumference edge closest to the casing 122) either flexible (e.g.,thinner) or sacrificial, with small sections breaking off if animpediment is encountered.

In some aspects, the brake 334 and one or more centralizers (such ascentralizers 314) may be employed on the hazardous material canister 320in order to increase a braking force on the canister 320 in free fall.For instance, with respect to the braking principle, a rapid flow of theliquid 336 may provide a force on the brake 334 and the brake 334 maythen cause the arms 316 of the centralizer 314 to be deployed withgreater force. In some aspects, one or more of the arms 316 may beconnected to the brake 334; thus, a force applied on the brake 334 mayurge the arms 316 into contact with the casing 122 or, if already incontact, against the casing 122 with greater force (e.g., normal to thecasing 122). In some aspects, the brake 334 may not be rigidly attachedto the housing 322 but may retain some movement axially along thehousing 322, e.g., to push against arms 316 of the centralizers 314.

FIG. 3C is a schematic illustration of a hazardous material canister 340according to the present disclosure. In some aspects, the hazardousmaterial canister 340 may be used as the hazardous material canister 126shown in the hazardous material storage repository system 100 of FIG. 1.In some aspects, the hazardous material canister 340 may enclose andstore nuclear or radioactive waste, such as SNF or high level waste. Asdescribed in the example emplacement process of the canisters 126 intothe hazardous material storage repository system 100 of FIG. 1, thehazardous material canister 340 may be placed in a human-unoccupiabledeep directional drillhole (e.g., drillhole 104) for long term (e.g.,hundreds if not thousands of years) storage. During the emplacementprocess, the hazardous material canister 340 may be moved into thedirectional drillhole 104 on a conveyance cable, such as, for example, awireline cable. When the hazardous material canister 340 is loweredthrough the vertical portion 106 of the directional drillhole 104, thereis a possibility that the cable (or a connection between the canister340 and the cable) that supports the canister 340 may fail. Uponfailure, the canister 340 will accelerate downward (e.g., in free fall)in the vertical portion 106 of the directional drillhole 104 (e.g.,through a fluid in the drillhole 104). Further, although notspecifically shown in FIG. 3C, the hazardous material canister 340 mayinclude certain components as described with reference to FIG. 2, suchas, for example, the material 216 and the impact absorber 252 (with orwithout a friction brake), as well as certain components as describedwith reference to FIG. 3B, such as, for example, the brake 334.

If the directional drillhole 104 has a kickoff point for the transitionportion 108 (e.g., a transition to a horizontal or nearly-horizontaldrillhole portion from the vertical portion 106), then the canister 340will slow and eventually stop in the horizontal drillhole portion 110.However, if the hazardous material storage repository system 100 haspreviously been filled with other hazardous material canisters 340, thenthe free-falling canister 340 could impact a stationary canister 340with resulting damage to both hazardous material canisters 340. If thehazardous waste material (e.g., nuclear waste) inside the canister 340is highly radioactive, there is a danger of release of this materialinto the drillhole portion 110, which could potentially lead to releaseinto a surrounding subterranean formation 118, and possibly mobile waterin such a formation or other formations (e.g., subterranean formation112). The illustrated implementation of hazardous material canister 340includes one or more features that, e.g., may reduce or preventpotential damage to the canister 340 due to a free-fall in the deepdirectional drillhole 104. For example, the hazardous material canister340 may maintain its structural integrity and its value as an“engineered barrier” to the release of hazardous material duringfree-fall and/or impact with another object in the drillhole 104.

As shown in FIG. 3C, the hazardous material canister 340 includes ahousing 342 that is comprised of a middle portion 344 to which a top (orlid) 346 and bottom 348 are coupled (e.g., subsequent to enclosing thehazardous waste) to form an inner volume 351. In this example, thehazardous material is one or more SNF assemblies 350 that include SNFrods (not specifically shown here). In this example, the hazardousmaterial canister 340 also includes two or more parachutes 352 that arecoupled to the housing 342, e.g., through rings 356 that circumscribe acircumference of the housing 342. In this example, therefore, a velocityof the hazardous material canister 340 in free-fall may be limited orreduced through the parachutes 352 driven by a high flow of the liquid354 in the drillhole 106 relative to the canister movement through thedrillhole 106 during free-fall.

In this example, the parachutes 352 may be broader on the leading end(e.g., on the downhole end of the canister 340). The broader sections ofthe parachutes 352, or “wings,” may be subject to a force that pushesthe connection point of the parachutes 352 and the ring 356 upward andthus may push the parachutes 352 more tightly against the inner surfaceof the casing 122 or, generally, spread out the parachutes 352 to createmore drag on the canister 340 during a free fall event. The force of thefluid 354 on the parachutes 352 may also provide force to reduce theacceleration of the canister 340 during free-fall.

FIG. 3D is a schematic illustration of a hazardous material canister 360according to the present disclosure. In some aspects, the hazardousmaterial canister 360 may be used as the hazardous material canister 126shown in the hazardous material storage repository system 100 of FIG. 1.In some aspects, the hazardous material canister 360 may enclose andstore nuclear or radioactive waste, such as SNF or high level waste. Asdescribed in the example emplacement process of the canisters 126 intothe hazardous material storage repository system 100 of FIG. 1, thehazardous material canister 360 may be placed in a human-unoccupiabledeep directional drillhole (e.g., drillhole 104) for long term (e.g.,hundreds if not thousands of years) storage. During the emplacementprocess, the hazardous material canister 360 may be moved into thedirectional drillhole 104 on a conveyance cable, such as, for example, awireline cable. When the hazardous material canister 360 is loweredthrough the vertical portion 106 of the directional drillhole 104, thereis a possibility that the cable (or a connection between the canister360 and the cable) that supports the canister 360 may fail. Uponfailure, the canister 360 will accelerate downward (e.g., in free fall)in the vertical portion 106 of the directional drillhole 104 (e.g.,through a fluid in the drillhole 104). Further, although notspecifically shown in FIG. 3D, the hazardous material canister 360 mayinclude certain components as described with reference to FIG. 2, suchas, for example, the material 216 and the impact absorber 252 (with orwithout a friction brake), as well as certain components as describedwith reference to FIG. 3A, 3B, or 3C, such as, for example, thecentralizers 314, the brake 334, and/or the parachutes 352.

If the directional drillhole 104 has a kickoff point for the transitionportion 108 (e.g., a transition to a horizontal or nearly-horizontaldrillhole portion from the vertical portion 106), then the canister 360will slow and eventually stop in the horizontal drillhole portion 110.However, if the hazardous material storage repository system 100 haspreviously been filled with other hazardous material canisters 360, thenthe free-falling canister 360 could impact a stationary canister 360with resulting damage to both hazardous material canisters 360. If thehazardous waste material (e.g., nuclear waste) inside the canister 360is highly radioactive, there is a danger of release of this materialinto the drillhole portion 110, which could potentially lead to releaseinto a surrounding subterranean formation 118, and possibly mobile waterin such a formation or other formations (e.g., subterranean formation112). The illustrated implementation of hazardous material canister 360includes one or more features that, e.g., may reduce or preventpotential damage to the canister 360 due to a free-fall in the deepdirectional drillhole 104. For example, the hazardous material canister360 may maintain its structural integrity and its value as an“engineered barrier” to the release of hazardous material duringfree-fall and/or impact with another object in the drillhole 104.

As shown in FIG. 3D, the hazardous material canister 360 includes ahousing 362 that is comprised of a middle portion 364 to which a top (orlid) 366 and bottom 368 are coupled (e.g., subsequent to enclosing thehazardous waste) to form an inner volume 372. In this example, thehazardous material is one or more SNF assemblies 370 that include SNFrods (not specifically shown here). In this example, the hazardousmaterial canister 360 also includes a foam (e.g., a porous material thatnaturally expands to fill a space) cover 374 that is formed around orattached (e.g., adhesively) around all, most, or some of the housing 362of the canister 360. In this example, the foam cover 374 covers most ofthe exterior of the housing 362, e.g., all but the lid 366. Inalternative implementations, the foam cover 374 may cover less of thehousing 362 (e.g., only a downhole end or portion) or as much as thewhole housing 362.

In some aspects, the foam cover 374 may be flexible enough that smalldiscontinuities in the casing 122 may compress the foam and allow thecanister 360 to be emplaced in the horizontal drillhole portion 110. Thefoam cover 374 may also offer resistance to fluid flow of the drillholefluid 376. Since the force of a liquid on an object (in the highReynold's number limit) is proportional to the square of the velocity ofthe object through the liquid, the fluid 376 may flow through and/oraround the foam cover 374 with little resistance when the canister 360is being slowly lowered into the vertical drillhole portion 106.However, if the canister 360 falls freely, the resistance of the foamcover 374 increases rapidly, and that increases the force of the flowingliquid 376 on the foam cover 374, which in turn acts to reduce theacceleration of the canister 360. The limiting velocity of the canister360 surrounded by the foam cover 374 may be substantially less than thelimiting velocity of a hazardous material canister that does not includethe foam cover 374.

The foam cover 374, in some implementations, may be made of the same (orsimilar) corrosion-resistant material as the housing 362 (all or part).For example, a metal material, such as a metal foam, may be used for thefoam cover 374. In some aspects, other components described with respectto the example implementations of the hazardous material canister canalso be made of the foam material (e.g., a metal foam). For instance,all or part of the impact absorber 252 and/or the brake 334 may be madeof the foam material (as with the foam cover 374).

FIGS. 4A-4B are schematic illustration of a hazardous material canister400 according to the present disclosure. FIG. 4A shows a schematicillustration of the canister 400, while FIG. 4B shows a detail of aportion of the canister 400. In some aspects, the hazardous materialcanister 400 may be used as the hazardous material canister 126 shown inthe hazardous material storage repository system 100 of FIG. 1. Further,in some aspects, the features described with reference to FIGS. 2 and3A-3D may also be implemented in the hazardous material canister 400shown in FIG. 4A. As described in the example emplacement process of thecanisters 126 into the hazardous material storage repository system 100of FIG. 1, the hazardous material canister 400 may be placed in ahuman-unoccupiable deep directional drillhole (e.g., drillhole 104) forlong term (e.g., hundreds if not thousands of years) storage.

In some aspects, the hazardous material canister 400 may enclose andstore nuclear or radioactive waste, such as SNF or high level waste. Forexample, when hazardous material (e.g., nuclear waste such as spentnuclear fuel or high level waste) is loaded into the hazardous materialcanister 400 (e.g., for storage in a human-unoccupiable, deepdirectional drillhole), the canister seal must be made secure againsteven miniscule leakage. Conventionally, this is done by welding the lid,followed by both visual and radiographic inspection, and a repair of thewelding if needed. In the cases of nuclear waste, if all this is done ina “hot cell” (e.g., a room a in which any escaped radionuclides can becollected and safely removed without escaping the room in an unwantedmanner), then the hot cell must be large and capable of incorporatingall the tasks including welding. Such large hot cells can be veryexpensive, particularly if they are designed to be portable for use atmultiple locations.

In some aspects, the loading of, e.g., spent nuclear fuel in thehazardous material canister 400 and then the sealing of that canister400 may proceed in a manner that will provide a barrier to escape ofradionuclides that will perform for thousands of years. Most of thespent nuclear fuel of interest is located in either cooling pools or drycasks, large concrete and steel containers that provide safety from thegamma radiation that spent fuel emits. Spent nuclear fuel consists ofpellets consisting primarily of uranium dioxide, but containing a largeinventory of highly radioactive fission fragments, transuranics such asplutonium and americium, and other radioactive elements created when thefuel was in the nuclear reactor. Removing the fuel assembly from a poolor dry cask and placing the fuel assembly in a canister for disposal maybe required to be performed in a hot cell in order to prevent therelease of radioisotopes to the environment (e.g., outside of the hotcell). Within the fuel assemblies, the radioisotopes are confined tolong tubes known as cladding, typically manufactured out of a metalalloy (such as zircalloy). The cladding provides isolation of theradioisotopes, and the main concern for safely moving the rods intocanisters is that the cladding may have lost integrity, e.g., that theremay be pinholes or cracks in the cladding that allow radionuclides toescape. For that reason, the transfer is typically done in the hot cell.A tiny hole in the fuel rod could allow radioactive krypton-85, forexample, to leak. Other radioisotopes that might leak include tritiumgas (hydrogen in which one or both hydrogen atoms are replaced with H₃),chlorine-36, and materials that become volatile at high temperature,such as iodine. In addition, small particles of the fuel pellets thatcould have separated from the pellets and formed a dust could leak ifthere is a sufficiently large hole or if the cladding has substantialdamage.

The hazardous material canister 400, for example, provides safetyagainst escape of radioisotopes when the fuel assembly or the fuelpellets are placed in an open housing of the canister while facilitatingthe sealing of two or more lids (or caps) on the housing. In someaspects, at least one of the lids may be sealed to the housing of thecanister outside of a hot cell. For example, as shown, the hazardousmaterial canister 400 includes a housing 402 that is comprised of amiddle portion 404 to which tops (or lids) 406 a and 406 b, as well as abottom 408 are coupled (e.g., subsequent to enclosing the hazardouswaste) to form an inner volume 412. In this example, the hazardousmaterial is one or more SNF assemblies 410 that include SNF rods (notspecifically shown here).

As shown more specifically in FIG. 4B, the hazardous material canister400 includes a seal that includes two separate barriers. For example,inner lid 406 b may be attached to the housing 402 of the hazardousmaterial canister 400. In some aspects, the inner lid 406 b is removablyattached to the housing 404, such as by mechanical attachment (e.g., athreaded attachment). For example, as shown, threads 416 may be formedon a portion of an inner radial surface of the middle portion 404 of thehousing 402. Threads 420 are also formed on a radial edge of the innerlid 406 b to mate (e.g., threadingly) with the housing 402. As shown, adiameter of the inner lid 406 b may be less than a diameter of outer lid406 a (and a diameter of the housing 402 at the threads 416).

In such examples, the inner lid 406 b may not be semi-permanently (e.g.,welded) in place in such a way as to require destruction of the innerlid 406 b or part of the housing 402 to remove the inner lid 406 b.Other example removable attachment techniques include use of a meltedmetal solder or an adhesive. The inner lid attachment may providesufficient safety for the canister 400 to be removed from the hot cellbut may not provide sufficient safety for the long term requirements fordisposal of the nuclear waste 410. In some aspects, the inner lid 406 bmay stay in place after the hazardous material canister 400 is placed ina hazardous waste repository in a deep, directional drillhole (such asin system 100).

In some aspects, the inner lid 406 b may not provide a seal thatprevents the leakage of radioactive waste for a long time, e.g.,hundreds if not thousands of years, but instead may facilitate removalof the hazardous material canister 400 from the hot cell. As shown inFIG. 4B, a seal 418 (e.g., a gasket such as a metal gasket) may bepositioned between the inner lid 406 b and the middle portion 404 (e.g.,at a shoulder 422 of the middle portion 404). In some aspects, thegasket 418 is put under sufficient pressure by the mechanical placementof the inner lid 406 b that the gasket 418 provides a seal of the innerlid 406 b to the housing 402 that provides a barrier for the escape ofradioactive material from the SNF assembly 410.

As shown, the shoulder 422 may separate a storage portion of the volume412 (e.g., below the shoulder 422 toward the bottom 408) from thethreaded portion 416. As shown, the storage portion has a smallerdiameter than the threaded portion 416 in this example.

As shown, outer lid 406 a is attached to the housing 402 subsequent toattachment of the inner lid 406 b. The outer lid 406 a, in some aspects,may provide greater safety against unwanted leakage of the radioactivewaste from the SNF assembly 410 by comprising a semi-permanent seal, forexample, by welding the outer lid 406 a to the housing 402. As shown inthis example, a weld 414 is created between the outer lid 406 a and atop radial edge of the housing 402, such as by spin welding. Althoughnot required, one or more of the components of the hazardous materialcanister 400, such as the housing 402 and the lids 406 a and 406 b, maybe made from similar materials (or the same material), such as acorrosion resistant alloy (e.g., CRA-625).

In some aspects, the hazardous material canister 400 (with the inner lid406 b attached) may be removed from a hot cell such that the outer lid406 a may be sealed to the housing 404 of the canister 400. In someaspects, the outer lid 406 a may be certified as providing an“engineered barrier” as required by a regulatory agency.

In an example operation of hazardous material canister 400, the SNFassembly 410 is placed in the inner volume 412 of the housing 402 (e.g.,which is open at a top end and may be enclosed with the bottom 408). Theplacement of the SNF assembly 410 may be in a hot cell. Subsequently,and still in the hot cell, the inner lid 406 b may be attached (e.g.,threadingly) to the housing 402 to seal the SNF assembly 410 within thevolume 412. The hazardous material canister 400 may then leave the hotcell, with only the inner lid 406 b in place (i.e., not the outer lid406 a). Outside the hot cell, the outer lid 406 a can be attached to thehousing 402 (e.g., by spin welding or otherwise). The sealed hazardousmaterial canister 400 may then be transported for emplacement in ahazardous waste repository system, such as system 100.

FIG. 5 is a schematic illustration of an example implementation of ahazardous material storage repository 500 that includes a safety runwayportion 502. As shown in FIG. 5, certain components of the hazardousmaterial storage repository 500 are the same as the hazardous materialstorage repository 100 shown in FIG. 1, such as, for example, a deep,human-unoccupiable directional drillhole 104 formed from the terraneansurface 102 through subterranean formations 112 through 118. As shown,the directional drillhole (or wellbore) 104 includes a verticaldrillhole portion 106 coupled to a transition, or radiussed, drillholeportion 108. The transition drillhole 108 is coupled to a horizontaldrillhole portion 110. In this example, the horizontal drillhole portion110 is inclined relative to “horizontal” such that a first end of thedrillhole portion 110 that is coupled to the transition drillhole 108 isdeeper (e.g., greater TVD) than a second end of the portion 110 oppositethe first end. Alternatively, the horizontal drillhole 110 may be closeto or exactly horizontal. In some aspects, all or part of thedirectional drillhole 104 may include a casing cemented in place.

As also described with reference to FIG. 1, hazardous material canisters126 that enclose hazardous material (e.g., nuclear waste such as SNF orhigh level waste) may be emplaced in a storage area 504 at the secondend of the horizontal drillhole portion 110. As described in the presentdisclosure, emplacement of hazardous material canisters 126 may includemoving the canisters 126 into the storage area 504, e.g., by a downholeconveyance, such as a tractor or by a force applied by coiled tubing ora working string (e.g., of threaded tubulars).

In some situations, a particular canister 126 could be accidentallyreleased from the downhole conveyance while the canister 126 is beinglowered into the directional drillhole 104. That could be due to aconsequence of failure of a latch that holds the canister 126 to theconveyance, or other reason. The canister 126 may then fall atincreasing velocity down the vertical portion 106 of the drillhole 104.This presents a danger that the canister 126 may collide with, e.g., apreviously-placed canister, and be damaged and will release hazardousmaterial into the drillhole 104 (and surrounding subterranean formations112-118). In some aspects, one or more features of the canister 126 canmitigate or prevent such damage, e.g., as shown in FIGS. 2 and 3A-3D.

The hazardous material storage repository 500 may, in some aspects, beoperable based on its design (independent of a design of the hazardousmaterial canisters 126 or other canisters) to bring a released canister126 to a safe stop, avoiding impacts with any object that could causedamage to the canister 126 (or other objects in the drillhole) orrelease of hazardous material from a damaged canister 126. As shown, thehazardous material storage repository 500 includes a safety runway 502that is a portion of the horizontal drillhole portion 110. The safetyrunway 502 is of sufficient length or inclination away (or both) fromhorizontal (e.g., toward the terranean surface 102), or both, to safelybring an improperly or accidentally released (and free-falling) canister126 to rest within the drillhole portion 110 without damaginglycontacting one or more hazardous material canisters 126 that are alreadyemplaced within the storage area 504.

In some aspects, the sufficient length and/or sufficient inclination maybe determined according to one or more test canisters (shown ashazardous material canisters 526) used in a constructed directionaldrillhole (e.g., the drillhole 104 or a similar “test” drillhole) thatincludes a storage area (e.g., storage area 504) formed in at least apart of the horizontal portion 110 of the drillhole 104. For example,before any hazardous material in placed in a storage area of a deep,directional drillhole, one or more test canisters 526 may be insertedinto the vertical portion of the drillhole from the terranean surfaceand purposefully allowed to fall freely into and through the verticalportion of the drillhole. The test canister 526 may be identical in allkey parameters to that of a hazardous waste canister that encloses waste(e.g., high level radioactive waste or spent nuclear fuel), except thatthe test canister 526 will enclose non-hazardous material (e.g., withthe same or similar weight as proposed hazardous waste). Thus, the testcanister 526 may match the disposal canister in weight, weightdistribution, and surface properties (such as coefficient of frictionand roughness for liquid flow). The drillhole, including the verticalportion, curved portion, and the horizontal or nearly horizontalportion, may be filled with the same fluid or gas that is present when adisposal canister would be inserted therein (if not already filled withsuch fluid). In some aspects, a “test” drillhole may transition to thedirectional drillhole 104 based on a successful test of the testcanisters 526 (and, in some aspects, meeting other criteria forsuitability as a hazardous waste repository).

The test canister 526 falls through the fluid in the drillhole,accelerating as it falls, and the test canister 526 may reach a terminalvelocity at which time the velocity will remain approximately constant.It may not be possible to calculate that terminal velocity explicitlysince the fluid flow around the test canister will likely be in aturbulent range, and insufficient analytic methods may exist todetermine such velocity under these conditions. The terminal velocitycan be estimated by using approximate methods and/or numericalsimulations; these suggest that the terminal velocity for a 1000 kg testcanister 526 will be about 10 meters per second (in the example here).However, the actual velocity of the test canister 526 may also bemeasured during free fall within the vertical portion of the directionaldrillhole.

When the test canister 526 enters the curved portion, and then thehorizontal (or nearly-horizontal) portion, it may slow from both fluidresistance and from friction with the walls of the drillhole (orcasing). The distance that the test canister 526 may travel depends atleast in part on the terminal velocity, the coefficient of friction ofthe exterior of the canister 526, and the upward tilt (if any) of thehorizontal portion of the directional drillhole. A “stopping distance”(also called the safety runway) may be determined that is a distancethat the test canister travels in the horizontal portion of thedrillhole until the canister comes to zero velocity, i.e., stops fromthe free fall.

As an example, if a terminal velocity of the test canister 526 is 10meters per second (m/s) and the coefficient of friction, k, is 0.1, astopping distance will be approximately 25 meters. In some aspects,according to dimensional analysis, the stopping distance will beapproximately proportional to the square of the terminal velocity. Thus,a length of the horizontal portion of the drillhole that includes thestorage area may be determined as a length of the repository in whichhazardous waste canisters (i.e., the storage area) are stored plus thestopping distance (or safety runway). For instance, for a 1 kmhorizontal portion of the drillhole, 25 meters may be the stoppingdistance portion (i.e., the safety runway), leaving 975 meters for therepository length. In this example, there is only a 4% loss (i.e.,percentage of safety runway length to length of storage area of thehorizontal portion of the drillhole). As another example, for a 3 kmhorizontal portion length and a 25 meter safety runway portion, canistercapacity in the storage area is reduced by only 1.33%.

As another example, if the terminal velocity of the test canister 526 is20 m/s, then the length of the safety runway would be about four timesgreater, and the reduced canister capacity would be increased byapproximately four times. Such estimates may be adjusted and determinedexperimentally by dropping one or more test canisters 526 into adrillhole.

As shown and described with reference to FIG. 5, the hazardous materialstorage repository 500 includes a horizontal drillhole portion 110 thatis inclined upward toward the terranean surface 102 (e.g., therebycausing the drillhole 104 to resemble a “j-” or “plumber's” trap). If apart of the horizontal portion 110 is tilted upward, then the stoppingdistance may be shorter, since the test canister 526 will be slowed bygravity as well as by friction. For example, if the terminal velocity is10 m/s, then gravity alone may stop the canister with a 5 meter rise. Insome aspects, the inclined part of the horizontal portion 110 (and alsothe transition from the curved portion 108 of the drillhole 104 to theinclined part of the horizontal portion 110) may act along with ahydraulic resistance and frictional force on the test canister 526 toreduce a length of the safety runway 502.

In some aspects, a terminal velocity of the test canister 526 maydecrease as soon as it enters the curved portion of the directionaldrillhole. For example, gravity may no longer act on the canister in thedirection of motion (i.e., vertically downward), which reduces agravitational force that is moving the canister 526 through thedrillhole. When the canister enters the curved portion, the canister maybe directed about 30° from horizontal, and therefore, not verticallydownward. The force of gravity may be reduced by about one-half, and theterminal velocity may be reduced by about 30%. When the terminalvelocity is reduced by 30%, then the length of the safety runway isreduced, in turn, by 50%. So the slowing of the canister 526 in thecurved portion of the drillhole can result in a significant reduction inthe length of the safety runway.

In some aspects, other techniques may be utilized to shorten a length ofthe safety runway 502. For example, a surface of the canister 126 (or acasing in the drillhole 104) could be purposefully roughened to increasethe coefficient of friction, k; such roughening could also affect theflow of fluids between the canister 126 and the casing (e.g., casing122) in such a way as to increase the hydrodynamic retarding force.However, in some circumstances, such roughening could decrease thehydrodynamic retarding force by increasing turbulence as well.

In some aspects, a canister capacity of the hazardous material storagerepository 500 is determined by a number of hazardous material canisters126 that can be emplaced within the storage area 504. Thus, thehorizontal portion 110 may include the storage area 504 (e.g., definedby a volume in which the canisters 126 are emplaced) and the safetyrunway 502 (e.g., defined by a volume in which no canisters 126 areemplaced). In some aspects, the safety runway portion is located at ornear a location of the drillhole in which a curved portion meets thehorizontal portion (e.g., near a “heel” of the directional drillhole)while the storage area is located near a “toe” of the directionaldrillhole (as shown in FIG. 5). In some aspects, a length of the safetyrunway portion may be determined based at least in part on an estimatedterminal velocity of the hazardous waste canister in the drillhole, afriction coefficient between the canister and the drillhole (or a casingin the drillhole), and, in some cases, an inclination deviation fromhorizontal of at least a part of the horizontal portion of thedrillhole. In some aspects, a length of the safety runway portion may bedetermined based at least in part on a recorded terminal velocity of atest hazardous waste canister in the drillhole, a friction coefficientbetween the test canister and the drillhole (or a casing in thedrillhole), and, in some cases, an inclination deviation from horizontalof at least a part of the horizontal portion of the drillhole. In someaspects, a length of the safety runway portion may be determined basedat least in part on a recorded stopping location of a test canister thatis allowed to free fall within the drillhole, with such a stoppinglocation being a particular distance (i.e., the safety runway distance)within the horizontal portion of the drillhole from the curved portionof the drillhole.

In some aspects, a directional drillhole formed to include the storagearea for the storage (or disposal) of canisters that enclose nuclearwaste as well as the safety runway may allow for a rapid delivery ofmultiple canisters into the repository. For example, the safety runwaymay reduce or eliminate the danger of damage to one or more canistersdue to a free falling canister within the drillhole. Thus, an initialhazardous waste canister (or set of canisters) may be emplaced into thestorage area of the horizontal portion of the drillhole by releasing thecanister(s) from the surface and allowing a quick descent at terminalvelocity through much of the drillhole. The initial canister or set ofcanisters would then come to rest in the horizontal portion of thedrillhole.

In some aspects of the aforementioned rapid delivery process, a downholetractor 530 (with power source) may be attached to a canister (or acanister within a set of canisters). The downhole tractor 530 may extendits wheels to make contact with the walls of the drillhole (or casing inthe drillhole) only when the canister has come to rest. Alternatively,the tractor wheels may be extended during free fall of the canister(s),and the resistance between the tractor wheels and the drillhole (orcasing) may reduce the velocity of the dropped canister(s).

Once the canister (or canisters) has come to rest, the tractor 530 wouldpush or pull the canister into a desired position within the hazardouswaste repository. For example, a canister that weighs about 1-ton mayrequire a pushing force from the downhole tractor 530 of about 1000Newtons. The energy to push the canister for a distance of 1 km could besupplied by a small battery weighing less than 2 kg, such as a 1.5 kgLithium-ion battery.

The downhole tractor 530 could be left in place, or it could beprogrammed to move back to the access hole. In an exampleimplementation, the downhole tractor 530 would then be retrieved to thesurface. In other example implementations, the downhole tractor 530would use the wheels in contact with the drillhole (or the casing) tocrawl upward and out of the hole. For a 10 kg tractor, includingbattery, the additional energy required to climb out would be about 30kWh, much less than the energy to push the canister one kilometer. Insome aspects, the downhole tractor 530 could be attached to acommunications cable that would indicate its location at all times. Thiscommunications cable would be light in weight, and it would be spun outso that there would be no force on it while the canister falls.

In some aspects of the present disclosure in which a safety runwaylength is determined through test canister 526 drops into the drillhole,after a first test canister 526 is dropped and retrieved, then a set oftest canisters 526 is dropped into the drillhole. The set of testcanisters 526 may be connected such as railroad cars are connected in astring of cars. The second set of test canisters 526 may be designed (byincreased mass and length) to slide deeper into the disposal region.After this test is done, and the set of test canisters 526 is removed(or left in place), sets of canisters 126 containing hazardous materialcan be dropped into the drillhole and carried by their velocity intomore distant parts of the storage area. The distance they travel wouldbe determined by their terminal velocity, which in turn is dependent ontheir mass, size, shape, and coefficient of friction.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinventions or of what may be claimed, but rather as descriptions offeatures specific to particular implementations of particularinventions. Certain features that are described in this specification inthe context of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresthat are described in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described program components and systemscan generally be integrated together in a single software product orpackaged into multiple software products.

A first example implementation according to the present disclosureincludes a hazardous material storage system that includes a drillholeextending into the Earth and including an entry at least proximate aterranean surface. The drillhole includes a substantially verticalportion, a curved portion, and a horizontal portion that includes ahazardous waste repository formed within a first portion of thehorizontal portion of the drillhole, the hazardous waste repositoryvertically isolated, by a rock formation, from a subterranean zone thatincludes mobile water, and a safety runway formed within a secondportion of the horizontal portion exclusive of the hazardous wasterepository and adjacent the curved portion, the safety runway defined bya particular length. The system further includes at least one hazardouswaste canister positioned in the hazardous waste repository. Thecanister is sized to fit from the drillhole entry through the vertical,the curved, and the horizontal portions of the drillhole, and into thehazardous waste repository. The hazardous waste canister includes aninner cavity sized to enclose hazardous material.

In an aspect combinable with the first example implementation, thehazardous waste includes nuclear waste.

In another aspect combinable with any of the previous aspects of thefirst example implementation, the nuclear waste includes at least one ofspent nuclear fuel or high level radioactive waste.

In another aspect combinable with any of the previous aspects of thefirst example implementation, the particular length is determined basedat least in part on a travel distance of the hazardous waste canister ora test canister into the horizontal portion from the vertical portionand through the curved portion in a free fall event.

In another aspect combinable with any of the previous aspects of thefirst example implementation, the travel distance is based at least inpart on a terminal velocity of the hazardous waste canister or the testcanister during the free fall event and a coefficient of frictionbetween the hazardous waste canister or the test canister and thedrillhole.

Another aspect combinable with any of the previous aspects of the firstexample implementation further includes an inclined portion of thedrillhole coupled between the curved portion and the horizontal portion.

In another aspect combinable with any of the previous aspects of thefirst example implementation, the particular length is determined basedat least in part on a travel distance of the hazardous waste canister ora test canister into the horizontal portion from the vertical portionand through the curved and inclined portions in a free fall event.

In another aspect combinable with any of the previous aspects of thefirst example implementation, the travel distance is based at least inpart on a terminal velocity of the hazardous waste canister or the testcanister during the free fall event, a coefficient of friction betweenthe hazardous waste canister or the test canister and the drillhole, andan angle of inclination of the inclined portion.

In another aspect combinable with any of the previous aspects of thefirst example implementation, the inclined portion is angled toward theterranean surface from the curved portion.

In another aspect combinable with any of the previous aspects of thefirst example implementation, the at least one hazardous waste canisteris positioned exclusively in the hazardous waste repository andexternally to the safety runway.

In another aspect combinable with any of the previous aspects of thefirst example implementation, the at least one hazardous waste canisterincludes a plurality of hazardous waste canisters.

In another aspect combinable with any of the previous aspects of thefirst example implementation, each of the plurality of hazardous wastecanisters is positioned exclusively in the hazardous waste repositoryand externally to the safety runway.

Another aspect combinable with any of the previous aspects of the firstexample implementation further includes a seal positioned in thedrillhole that isolates the hazardous waste repository from the entry ofthe drillhole.

A second example implementation according to the present disclosureincludes a method for storing hazardous waste that includes moving ahazardous waste canister through an entry of a drillhole that extendsinto a terranean surface. The entry is at least proximate the terraneansurface, and the hazardous waste canister includes an inner cavity thatencloses hazardous waste. The method further includes moving thehazardous waste canister through a vertical portion of the drillhole andthrough a curved portion of the drillhole; moving the hazardous wastecanister from the curved portion through a first part of a horizontalportion of the drillhole that includes a safety runway defined by aparticular length; and moving the hazardous waste canister from thefirst part of the horizontal portion of the drillhole into a second partof the horizontal portion of the drillhole that includes a hazardouswaste repository. The hazardous waste canister is sized to fit from thedrillhole entry through the vertical, the curved, and the horizontalportions of the drillhole. The hazardous waste repository is verticallyisolated, by a rock formation, from a subterranean zone that includesmobile water.

In an aspect combinable with the second example implementation, thehazardous waste includes nuclear waste.

In another aspect combinable with any of the previous aspects of thesecond example implementation, the nuclear waste includes at least oneof spent nuclear fuel or high level radioactive waste.

In another aspect combinable with any of the previous aspects of thesecond example implementation, the particular length is determined basedat least in part on a travel distance of the hazardous waste canister ora test canister into the horizontal portion from the vertical portionand through the curved portion in a free fall event.

In another aspect combinable with any of the previous aspects of thesecond example implementation, the travel distance is based at least inpart on a terminal velocity of the hazardous waste canister or the testcanister during the free fall event and a coefficient of frictionbetween the hazardous waste canister or the test canister and thedrillhole.

Another aspect combinable with any of the previous aspects of the secondexample implementation further includes an inclined portion of thedrillhole coupled between the curved portion and the horizontal portion.

In another aspect combinable with any of the previous aspects of thesecond example implementation, the particular length is determined basedat least in part on a travel distance of the hazardous waste canister ora test canister into the horizontal portion from the vertical portionand through the curved and inclined portions in a free fall event.

In another aspect combinable with any of the previous aspects of thesecond example implementation, the travel distance is based at least inpart on a terminal velocity of the hazardous waste canister or the testcanister during the free fall event, a coefficient of friction betweenthe hazardous waste canister or the test canister and the drillhole, andan angle of inclination of the inclined portion.

In another aspect combinable with any of the previous aspects of thesecond example implementation, the inclined portion is angled toward theterranean surface from the curved portion.

In another aspect combinable with any of the previous aspects of thesecond example implementation, the at least one hazardous waste canisteris positioned exclusively in the hazardous waste repository andexternally to the safety runway.

In another aspect combinable with any of the previous aspects of thesecond example implementation, the at least one hazardous waste canisterincludes a plurality of hazardous waste canisters.

In another aspect combinable with any of the previous aspects of thesecond example implementation, each of the plurality of hazardous wastecanisters is positioned exclusively in the hazardous waste repositoryand externally to the safety runway.

Another aspect combinable with any of the previous aspects of the secondexample implementation further includes positioning a seal in thedrillhole that isolates the hazardous waste repository from the entry ofthe drillhole.

A third example implementation according to the present disclosureincludes a nuclear waste canister that includes a housing that includesa closed end and an open end opposite the closed end. The housingdefines an inner volume sized to hold at least one nuclear wasteportion. The housing is configured to store nuclear waste in ahuman-unoccupiable directional drillhole. The canister includes a firstlid attachable to the housing between the closed end and the open end tocreate a first seal of the inner volume; and a second lid attachable tothe housing at or near the open end to create a second seal of the innervolume.

In an aspect combinable with the third example implementation, thenuclear waste portion includes a spent nuclear fuel assembly.

In another aspect combinable with any of the previous aspects of thethird example implementation, the outer housing includes a corrosionresistant alloy.

In another aspect combinable with any of the previous aspects of thethird example implementation, the corrosion resistant alloy includes CRA625.

In another aspect combinable with any of the previous aspects of thethird example implementation, the first lid is configured tomechanically attach to the housing.

In another aspect combinable with any of the previous aspects of thethird example implementation, the first lid is configured to threadinglyattach to the housing.

In another aspect combinable with any of the previous aspects of thethird example implementation, the housing includes an inner surface thatincludes a threaded portion between the open end and the closed end.

In another aspect combinable with any of the previous aspects of thethird example implementation, the inner surface includes a smoothportion between the closed end and the threaded portion.

In another aspect combinable with any of the previous aspects of thethird example implementation, the inner volume includes a firstcross-sectional dimension at the smooth portion of the inner surface anda second cross-sectional dimension greater than the firstcross-sectional dimension at the threaded portion of the inner surface.

Another aspect combinable with any of the previous aspects of the thirdexample implementation further includes a gasket positioned between aportion of the housing and the first lid.

In another aspect combinable with any of the previous aspects of thethird example implementation, the gasket includes a metal gasket.

In another aspect combinable with any of the previous aspects of thethird example implementation, the second lid is attachable to thehousing at the open end.

In another aspect combinable with any of the previous aspects of thethird example implementation, the second lid is attachable to thehousing at or near the open end with a weld.

In another aspect combinable with any of the previous aspects of thethird example implementation, the weld includes a spin weld.

In another aspect combinable with any of the previous aspects of thethird example implementation, the first lid is attachable to the housingwithin a hot cell, and the second lid is attachable to the housingoutside of the hot cell.

A fourth example implementation according to the present disclosureincludes a method for containing nuclear waste that includes placing atleast one nuclear waste portion into an inner volume of a housing of anuclear waste canister. The housing includes a closed end and an openend opposite the closed end. The housing is configured to store nuclearwaste in a human-unoccupiable directional drillhole. The method furtherincludes attaching a first lid to the housing between the closed end andthe open end to create a first seal of the inner volume; and attaching asecond lid to the housing at or near the open end to create a secondseal of the inner volume.

In an aspect combinable with the fourth example implementation, thenuclear waste portion includes a spent nuclear fuel assembly.

In another aspect combinable with any of the previous aspects of thefourth example implementation, the outer housing includes a corrosionresistant alloy.

In another aspect combinable with any of the previous aspects of thefourth example implementation, the corrosion resistant alloy includesCRA 625.

In another aspect combinable with any of the previous aspects of thefourth example implementation, attaching the first lid includesmechanically attaching the first lid to the housing.

In another aspect combinable with any of the previous aspects of thefourth example implementation, mechanically attaching the first lidincludes threadingly attaching the first lid to the housing.

In another aspect combinable with any of the previous aspects of thefourth example implementation, threadingly attaching the first lid tothe housing includes screwing the first lid to an inner surface thatincludes a threaded portion between the open end and the closed end.

In another aspect combinable with any of the previous aspects of thefourth example implementation, the inner surface includes a smoothportion between the closed end and the threaded portion.

In another aspect combinable with any of the previous aspects of thefourth example implementation, the inner volume includes a firstcross-sectional dimension at the smooth portion of the inner surface anda second cross-sectional dimension greater than the firstcross-sectional dimension at the threaded portion of the inner surface.

Another aspect combinable with any of the previous aspects of the fourthexample implementation further includes a gasket positioned between aportion of the housing and the first lid.

In another aspect combinable with any of the previous aspects of thefourth example implementation, the gasket includes a metal gasket.

In another aspect combinable with any of the previous aspects of thefourth example implementation, attaching the second lid to the housingat or near the open end includes attaching the second lid to the housingat the open end.

In another aspect combinable with any of the previous aspects of thefourth example implementation, attaching the second lid includes weldingthe second lid to the housing at or near the open end.

In another aspect combinable with any of the previous aspects of thefourth example implementation, welding the second lid includes spinwelding the second lid to the housing.

In another aspect combinable with any of the previous aspects of thefourth example implementation, the step of attaching the first lidoccurs within a hot cell, and the step of attaching the second lidoccurs outside of the hot cell.

A fifth example implementation according to the present disclosureincludes a nuclear waste disposal system that includes a nuclear wastecanister including a housing that defines an interior volume sized toenclose nuclear waste. The nuclear waste canister is configured to storethe nuclear waste in a human-unoccupiable directional drillhole in asubterranean formation beneath a terranean surface. The system furtherincludes a free-fall limiting device mounted on the nuclear wastecanister configured to slow a velocity of the canister during free-fallmovement of the canister in the drillhole.

In an aspect combinable with the fifth example implementation, thenuclear waste includes spent nuclear fuel.

In another aspect combinable with any of the previous aspects of thefifth example implementation, the spent nuclear fuel includes at leastone spent nuclear fuel assembly.

In another aspect combinable with any of the previous aspects of thefifth example implementation, the free-fall limiting device includes acentralizer mounted on the nuclear waste canister.

In another aspect combinable with any of the previous aspects of thefifth example implementation, the centralizer includes a plurality ofexpandable arms configured to adjust radially away from the housing tocontact the drillhole during free-fall movement of the canister in thedrillhole.

In another aspect combinable with any of the previous aspects of thefifth example implementation, the plurality of expandable arms areconfigured to adjust radially away from the housing based at least inpart on a fluid force acting on the arms during free-fall movement ofthe canister in the drillhole.

Another aspect combinable with any of the previous aspects of the fifthexample implementation further includes a disc mounted on a downhole endof the canister.

In another aspect combinable with any of the previous aspects of thefifth example implementation, the disc is configured to increase a fluidforce acting on the arms during free-fall movement of the canister inthe drillhole.

In another aspect combinable with any of the previous aspects of thefifth example implementation, the free-fall limiting device includes oneor more parachute arms mounted on a downhole end of the canister.

In another aspect combinable with any of the previous aspects of thefifth example implementation, the parachute arms are configured toincrease a fluid force acting on the arms during free-fall movement ofthe canister in the drillhole.

In another aspect combinable with any of the previous aspects of thefifth example implementation, the free-fall limiting device includes afoam member mounted on the canister.

In another aspect combinable with any of the previous aspects of thefifth example implementation, the foam member is configured to increasea fluid force acting on the foam member during free-fall movement of thecanister in the drillhole.

Another aspect combinable with any of the previous aspects of the fifthexample implementation further includes at least one impact absorbermounted on the canister.

In another aspect combinable with any of the previous aspects of thefifth example implementation, the impact absorber is mounted on adownhole end of the canister.

A sixth example implementation according to the present disclosureincludes a method for impeding a free-falling nuclear waste canisterthat includes moving a nuclear waste canister through a directionaldrillhole from a terranean surface toward a subterranean zone on acable, the nuclear waste canister configured to store nuclear waste; andbased on the nuclear waste canister experiencing a free-fall event uponbeing detached from the cable, limiting a free-fall velocity of thecanister in the drillhole with a free-fall limiting device mounted onthe nuclear waste canister.

In an aspect combinable with the sixth example implementation, thenuclear waste includes spent nuclear fuel.

In another aspect combinable with any of the previous aspects of thesixth example implementation, the spent nuclear fuel includes at leastone spent nuclear fuel assembly.

In another aspect combinable with any of the previous aspects of thesixth example implementation, the free-fall limiting device includes acentralizer mounted on the nuclear waste canister.

In another aspect combinable with any of the previous aspects of thesixth example implementation, limiting the free-fall velocity of thecanister in the drillhole includes radially adjusting a plurality ofexpandable arms on the centralizer to contact the drillhole duringfree-fall movement of the canister in the drillhole.

In another aspect combinable with any of the previous aspects of thesixth example implementation, the plurality of expandable arms areconfigured to adjust radially away from the housing based at least inpart on a fluid force acting on the arms during free-fall movement ofthe canister in the drillhole.

Another aspect combinable with any of the previous aspects of the sixthexample implementation further includes a disc mounted on a downhole endof the canister.

In another aspect combinable with any of the previous aspects of thesixth example implementation, the disc is configured to increase a fluidforce acting on the arms during free-fall movement of the canister inthe drillhole.

In another aspect combinable with any of the previous aspects of thesixth example implementation, the free-fall limiting device includes oneor more parachute arms mounted on a downhole end of the canister.

In another aspect combinable with any of the previous aspects of thesixth example implementation, limiting the free-fall velocity of thecanister in the drillhole includes increasing a fluid force acting onthe arms during free-fall movement of the canister in the drillhole.

In another aspect combinable with any of the previous aspects of thesixth example implementation, the free-fall limiting device includes afoam member mounted on the canister.

In another aspect combinable with any of the previous aspects of thesixth example implementation, limiting the free-fall velocity of thecanister in the drillhole includes increasing a fluid force acting onthe foam member during free-fall movement of the canister in thedrillhole.

Another aspect combinable with any of the previous aspects of the sixthexample implementation further includes at least one impact absorbermounted on the canister.

In another aspect combinable with any of the previous aspects of thesixth example implementation, the impact absorber is mounted on adownhole end of the canister.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without departingfrom the spirit and scope of the disclosure. For example, while manyexample implementations of a hazardous material canister according tothe present disclosure include a cross-section that is circular or oval,other shapes are contemplated, such as square or rectangular. Also,example operations, methods, or processes described herein may includemore steps or fewer steps than those described. Further, the steps insuch example operations, methods, or processes may be performed indifferent successions than that described or illustrated in the figures.Accordingly, other implementations are within the scope of the followingclaims.

What is claimed is:
 1. A nuclear waste canister, comprising: a housingthat at least partially defines an inner volume sized to enclose aplurality of nuclear waste portions and configured to store the nuclearwaste portions in a hazardous waste repository of a directionaldrillhole formed in a subterranean formation; a solid or semi-solidgranular material enclosed in the inner volume of the housing that atleast substantially fills voids within the inner volume and between theplurality of nuclear waste portions; and a friction brake mounted to anend of the housing.
 2. The nuclear waste canister of claim 1, whereinthe nuclear waste portions comprise a plurality of spent nuclear fuel(SNF) rods of an SNF assembly.
 3. The nuclear waste canister of claim 2,wherein the inner volume is sized to store a single SNF assembly.
 4. Thenuclear waste canister of claim 1, wherein the solid or semi-solidgranular material comprises a solid powder.
 5. The nuclear wastecanister of claim 4, wherein the solid powder comprises silicon-dioxide.6. The nuclear waste canister of claim 1, wherein the solid orsemi-solid granular material comprises a neutron-absorbing material. 7.The nuclear waste canister of claim 1, further comprising an impactabsorber positioned within the inner volume or on an exterior surface ofthe housing.
 8. The nuclear waste canister of claim 7, wherein theimpact absorber comprises a crushable member or spring member.
 9. Thenuclear waste canister of claim 7, wherein the impact absorber comprisesa corrosion-resistant material.
 10. The nuclear waste canister of claim1, wherein the friction brake is mounted to the housing with a pivotableor rotatable connection.
 11. The nuclear waste canister of claim 1,wherein the end of the housing comprises a downhole end of the housing.12. The nuclear waste canister of claim 1, wherein the friction brakecomprises a surface configured to contact a casing installed in thedirectional drillhole.
 13. A method for storing nuclear waste,comprising: placing a plurality of nuclear waste portions into an innervolume of a housing of a nuclear waste canister configured to store thenuclear waste portions in a hazardous waste repository of a directionaldrillhole formed in a subterranean formation, wherein the nuclear wastecanister comprises a friction brake mounted to an end of the housing;substantially filling voids within the inner volume and between theplurality of nuclear waste portions with a solid or semi-solid granularmaterial; and sealing the inner volume of the nuclear waste canister toenclose the plurality of nuclear waste portions and the solid orsemi-solid granular material.
 14. The method of claim 13, wherein thenuclear waste portions comprise a plurality of spent nuclear fuel (SNF)rods of an SNF assembly.
 15. The method of claim 14, wherein the innervolume is sized to store a single SNF assembly.
 16. The method of claim13, wherein the solid or semi-solid granular material comprises a solidpowder.
 17. The method of claim 16, wherein the solid powder comprisessilicon-dioxide.
 18. The method of claim 13, wherein the solid orsemi-solid granular material comprises a neutron-absorbing material. 19.The method of claim 13, wherein the nuclear waste canister furthercomprises an impact absorber positioned within the inner volume or on anexterior surface of the housing.
 20. The method of claim 19, wherein theimpact absorber comprises a crushable member or spring member.
 21. Themethod of claim 19, wherein the impact absorber comprises acorrosion-resistant material.
 22. The method of claim 13, wherein thefriction brake is mounted to the housing with a pivotable or rotatableconnection.
 23. The method of claim 13, wherein the end of the housingcomprises a downhole end of the housing.
 24. The method of claim 13,wherein the friction brake comprises a surface configured to contact acasing installed in the directional drillhole.
 25. The method of claim13, further comprising moving the sealed nuclear waste canister into thehazardous waste repository of the directional drillhole.
 26. The methodof claim 25, further comprising mitigating an impact of the sealednuclear waste canister during a free fall event during movement of thesealed nuclear waste canister through the directional drillhole.
 27. Themethod of claim 26, wherein mitigating the impact of the sealed nuclearwaste canister during the free fall event during movement of the sealednuclear waste canister through the directional drillhole comprisescontacting a portion of the directional drillhole or a wellbore fluidwith the friction brake during the free fall event.
 28. The method ofclaim 27, wherein contacting the portion of the directional drillhole orthe wellbore fluid with the friction brake during the free fall eventcomprises contacting a casing positioned in the directional drillholewith the friction brake during the free fall event.